A laser machining apparatus for machining, such as cutting, boring, welding, surface-treating, a material using laser beam is advantageous in freely selecting a desired machined shape and is therefore widely used particularly as machining means for manufacturing a little amount of variety of products. FIG. 1 schematically shows a conventional laser beam machine using carbon-dioxide gas.
In FIG. 1, the laser beam machine 1 is equipped with a carbon-dioxide gas laser oscillator 2 as a laser beam supply source. Laser beam LB outputted from the carbon-dioxide gas laser oscillator 2 reaches a main machining unit 4 via a non-illustrated shield-light duct and is then transmitted to a machining head 5 of the main machining unit 4 via mirrors M1, M2.
A condenser lens (not shown) is mounted in the machining head 5 so that the light refracted downwardly by the mirror M2 is gathered and concentrated by the condenser lens, whereupon the concentrated light is projected on a workpiece W from a machining nozzle 6 mounted on a tip of the machining head 5. In order to improve a machining speed and a degree of the machined surface roughness, it has been a common practice to blow assist gas to the machining surface from an assist gas nozzle attached to the machining head 5.
A machining point on which laser beam LB strikes is disposed just under a machining nozzle 6 of the machining head 5. Accordingly, the position of this machining point is determined by positioning the machining head 5 with respect to the X axis and the Y axis. In order to obtain a desired shape of the machined workpiece, the machining head 5 is mounted on an X-Y drive mechanism. The X-Y drive mechanism is a mechanism for moving the machining head 5 in a straight line in .+-.X-axis direction and .+-.Y-axis direction and typically comprises a ball screw 6A for X-axis driving, a linear bearing 6B, a servo motor 7, a ball screw 8 for Y-axis driving, and a servo motor 9.
Each servo motor 7, 9 is usually controlled by a computerized numerical controller (CNC) 3. As a playback operation is carried out after teaching a machining program to the numerical controller 3, the machining head 5 is positioned at positions on X-axis and Y-axis (or X-axis, Y-axis and Z-axis positions) in order corresponding to position data contained in the machining program so that machining is accomplished according to the desired shape designated by the machining program.
The Z-axis position of the machining head 5 is often made adjustable independently by a suitable Z-axis moving mechanism. Alternatively, the same control as the X-axis and Y-axis control may be performed using a servo motor and a numerical controller. Instead of moving the machining head 5 by the X-Y drive mechanism, it is also known to move a worktable for mounting a workpiece by the X-Y drive mechanism.
However, the conventional laser machining apparatus utilizing the above-mentioned serial X-Y drive system is not advantageous in quickly moving the machining point as its machining speed is low as compared to other machining tools such as punch press. Namely, if the machining head is moved at a high speed, the degree of rigidity of various constituent members does not conform such high-speed moving so that only inadequate machining accuracy can be achieved. If the degree of rigidity of the individual constituent members was increased in an effort to avoid lowering of the machining accuracy, the load on the drive mechanism would have increased in moving the machining head, which requires a large-sized drive mechanism and hence cannot be a practical solution.